1. Field of the Invention
This invention relates to vehicle engine fuel supply systems and, particularly, to a fuel supply system having a reserve fuel container and fuel pump located within the vehicle fuel tank.
2. Description of Prior Developments
It is known to provide a fuel container in a vehicle fuel tank for supplying fuel to a fuel pump when the tank is essentially empty, or when the fuel in the tank is sloshing or thrown away from the pump inlet chamber due to vehicle turning maneuvers.
U.S. Pat. No. 4,974,570 to Szwargulski shows a reserve fuel supply system that includes a pressure responsive valve for conveying fuel from a reserve container to the fuel pump when a float valve in the tank closes due to lack of fuel in the tank. The reserve fuel container has an open top such that fuel vapors associated with heated fuel can circulate between the reserve container and the surrounding space in the fuel tank.
Conventional engine fuel systems have fuel pumps that are sized to deliver more fuel than the engine can use. Excess fuel not used by the engine is returned to the fuel tank via a return line. The excess fuel is usually heated as a result of its travel through the engine fuel injectors or other heated passageways. Consequently, the returned fuel tends to heat the fuel in the tank.
Under some conditions, fuel vapors from the heated fuel can form in the tank to such an extent that, when the motorist opens the gas cap on the tank to add fuel, the accumulated vapors can escape into the ambient atmosphere. Such vapor escape represents an air pollution problem that the present invention is designed to reduce.
Fuel supply systems having reserve fuel containers within the fuel tanks are disclosed in various patents, e.g., U.S. Pat. Nos. 3,443,519; 4,672,937; 4,747,388; 4,776,315; 4,807,582; and 4,831,990. It is not believed that any of these patent disclosures address the problem of fuel vapor accumulation and vapor escape from the fuel tank.